Qt之插件

插件结构

QPluginLoader：用于运行时加载插件

• instance()方法获取插件的根组件,先使用load()加载库得到instanceFactory，然后调用该工厂方法创建实例
• metaData方法获取插件的元数据，内部是QLibraryPrivate调用库的qt_plugin_query_metadata方法来获取
• load()方法是从库获取方法qt_plugin_instance，并且存在instanceFactory变量中
• unload()方法是卸载库，windows下是调用FreeLibrary，linux是调用dlclose，然后复位pHnd和instanceFactory
• isLoaded()方法看是否加载完成，主要是看instanceFactory是否不为空
• staticInstances()方法获取全局变量staticPluginList的实例副本
• staticPlugins()获取全局变量staticPluginList

QLibrary：运行时加载动态库

• resolve：解析得到函数指针
• load：加载库
• unload：卸载库
• isLoaded：库是否加载完成

QLibraryStore：用于存储库名与QLibraryPrivate 映射关系

静态插件

注册

通过qRegisterStaticPluginFunction将静态插件添加到类型为StaticPluginList的全局变量中

typedef QVector<QStaticPlugin> StaticPluginList;
Q_GLOBAL_STATIC(StaticPluginList, staticPluginList)

void Q_CORE_EXPORT qRegisterStaticPluginFunction(QStaticPlugin staticPlugin)
{
	staticPluginList()->append(plugin);
}

静态插件的创建是通过宏QT_MOC_EXPORT_PLUGIN

#if QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
#  define QT_MOC_EXPORT_PLUGIN(PLUGINCLASS, PLUGINCLASSNAME) \
    static QT_PREPEND_NAMESPACE(QObject) *qt_plugin_instance_##PLUGINCLASSNAME() \
    Q_PLUGIN_INSTANCE(PLUGINCLASS) \
    static QPluginMetaData qt_plugin_query_metadata_##PLUGINCLASSNAME() \
        { return { qt_pluginMetaData, sizeof qt_pluginMetaData }; } \
    const QT_PREPEND_NAMESPACE(QStaticPlugin) qt_static_plugin_##PLUGINCLASSNAME() { \
        return { qt_plugin_instance_##PLUGINCLASSNAME, qt_plugin_query_metadata_##PLUGINCLASSNAME}; \
    }
#else
#  define QT_MOC_EXPORT_PLUGIN(PLUGINCLASS, PLUGINCLASSNAME) \
    static QT_PREPEND_NAMESPACE(QObject) *qt_plugin_instance_##PLUGINCLASSNAME() \
    Q_PLUGIN_INSTANCE(PLUGINCLASS) \
    static const char *qt_plugin_query_metadata_##PLUGINCLASSNAME() { return reinterpret_cast<const char *>(qt_pluginMetaData); } \
    const QT_PREPEND_NAMESPACE(QStaticPlugin) qt_static_plugin_##PLUGINCLASSNAME() { \
        QT_PREPEND_NAMESPACE(QStaticPlugin) plugin = { qt_plugin_instance_##PLUGINCLASSNAME, qt_plugin_query_metadata_##PLUGINCLASSNAME}; \
        return plugin; \
    }
#endif

宏Q_PLUGIN_INSTANCE用于创建全局的插件实例

#define Q_PLUGIN_INSTANCE(IMPLEMENTATION) \
        { \
            static QT_PREPEND_NAMESPACE(QPointer)<QT_PREPEND_NAMESPACE(QObject)> _instance; \
            if (!_instance) {    \
                QT_PLUGIN_RESOURCE_INIT \
                _instance = new IMPLEMENTATION; \
            } \
            return _instance; \
        }

静态插件注册到全局变量中是通过宏Q_IMPORT_PLUGIN

#define Q_IMPORT_PLUGIN(PLUGIN) \
        extern const QT_PREPEND_NAMESPACE(QStaticPlugin) qt_static_plugin_##PLUGIN(); \
        class Static##PLUGIN##PluginInstance{ \
        public: \
                Static##PLUGIN##PluginInstance() { \
                    qRegisterStaticPluginFunction(qt_static_plugin_##PLUGIN()); \
                } \
        }; \
       static Static##PLUGIN##PluginInstance static##PLUGIN##Instance;

QFactoryLoader结构

QFactoryLoader管理多个QLibraryPrivate

update：从应用的库目标集合中加载创建库，从库的元数据中获取IID，Keys,对应添加到QFactoryLoaderPrivate中的iid, loadedPaths, libraryList以及keyMap中
QFactoryLoader构造函数：会将自身添加到全局变量Q_GLOBAL_STATIC(QList<QFactoryLoader *>, qt_factory_loaders)中
refreshAll：遍历全局变量qt_factory_loaders，调用update方法更新库信息
metaData：获取libraryList以及全局静态插件staticPlugins的元数据信息列表
instance：从libraryList和全局静态插件staticPlugins获取index位置 的插件实例，libraryList在前，静态插件staticPlugins在后
keyMap：先调用metaData得到所有插件的元数据，遍历获取所有的Keys字段的数据
indexOf：获取元数据列表中keys元素等于needle的元数据列表中的索引

模板函数

qLoadPlugin通过QFactoryLoader以及key来得到对应的工厂方法，然后调用create方法创建对应的QFactoryInterface

template <class PluginInterface, class FactoryInterface, typename ...Args>
PluginInterface *qLoadPlugin(const QFactoryLoader *loader, const QString &key, Args &&...args)
{
    const int index = loader->indexOf(key);
    if (index != -1) {
        QObject *factoryObject = loader->instance(index);
        if (FactoryInterface *factory = qobject_cast<FactoryInterface *>(factoryObject))
            if (PluginInterface *result = factory->create(key, std::forward<Args>(args)...))
                return result;
    }
    return nullptr;
}